As I recall, it's just a I-IV-V w/ power chords. Here it is in E.
(I don't remember if that's the original key or not, if not, try C or D)
It starts with a pick slide then:
E E E E B B B B A A A A E E E E in rhythm.
The "interlude" part is just those same chords arpeggiated, and the
"reggae" part with the humming is the same exact chords with an echo/delay
and a backbeat feel.
What the hell was I thinking. . . . What I posted before was in A'.
Here are the proper chords for P.D in E:
Textes des accords STRADLIN IZZY Pressure Drop. Skitarrate pour jouer votre musique, l'ètude des 'èchelles, des positions pour guitare, la recherche, la gestion, la demande et envoyer accords, paroles et partitions